A minimal quantity lubrication technology is also called as an MQL (Minimal Quantity Lubrication) technology, which is used for mixing and atomizing minimal quantity lubricant and compressed air with certain pressure, and spraying the mixture to a grinding area to effectively lubricate contact surfaces between a grinding wheel and abrasive dust and between the grinding wheel and a workpiece. Under the premise of ensuring effective lubricating and cooling effects, minimal grinding liquid (about parts per thousand of the consumption of a traditional pouring-type lubricating manner) is used in the technology, to reduce cost, pollution to the environment and harm to human bodies.
Nano particles jet minimal quantity lubrication is established on the basis of the enhanced heat exchange theory, and it could be known from the enhanced heat exchange theory that the heat transfer capability of solid is further greater than that of liquid and gas. The heat conductivity coefficient of a solid material at normal temperature is a few orders of magnitude greater than that of a fluid material. By adding solid particles into a minimal quantity lubrication medium, the heat conductivity coefficient of a fluid medium may be significantly improved, the capability of convection heat transfer may be improved, and the defect of insufficient minimal quantity lubrication cooling capability is greatly overcome. Moreover, nano particles (indicating superfine minimal solid particles of which the size is 1-100 nm) also have special tribological properties of wear resistance, friction reduction, high bearing capability and the like in the aspects of lubrication and tribology. The nano jet minimal quantity lubrication indicates that nano-scale solid particles are added into a minimal quantity lubrication fluid medium to prepare nano fluid, namely nano particles, lubricant (oil or oil-water mixture) and high pressure gas are mixed and atomized and then sprayed to a grinding area in the form of jet flow.
Inventors carried out deep theoretical analysis and experimental verification on a minimal quantity lubrication grinding liquid supply system, and have applied for relevant patents with respect to the research results. The invention patent with an application number of 201210153801.2 applied by the invention designers discloses a nano particle jet minimal quantity lubrication grinding liquid supply system, wherein nano solid particles are added into degradable grinding liquid to prepare a minimal quantity lubrication grinding liquid, the lubricant is turned into pulse liquid drops with fixed pressure, variable pulse frequency and invariable liquid drop diameter by a minimal quantity supply device, and the pulse liquid drops are sprayed in the form of jet flow to a grinding area under the action of an air isolating layer generated by high pressure gas. However, in the invention patent with an application number of 201210153801.2, jet flow controllable minimal liquid drops are not produced in the form of electrostatic atomization, and the atomization principle and the liquid drop control manner are different. The invention patent with an application number of 201110221543.2 discloses a nano particle jet flow minimal quantity lubrication grinding three-phase stream supply system, wherein nano fluid is conveyed to a nozzle through a liquid path, meanwhile, high pressure gas enters the nozzle through a gas path, the high pressure gas and the nano fluid are fully mixed and atomized in a mixing chamber of the nozzle, are accelerated in an accelerating chamber and then enter a swirl chamber, meanwhile, compressed gas enters from vents of the swirl chamber, the three-phase stream is further mixed and accelerated by rotating, and then the three-phase stream is sprayed in the form of atomized liquid drops to a grinding area through the outlet of the nozzle. However, in the disclosed technical scheme, charged minimal fog drops are also not formed by adopting the principle of electrostatic atomization, controllable jet flow may not be realized, and the atomization principle and the liquid drop control manner are different.
At present, the minimal quantity lubricant in the minimal quantity lubrication grinding may not be effectively and controllably injected into the grinding area, namely a wedge-shaped area of a grinding wheel/workpiece interface under the carrying effect of the high pressure gas, so nano jet flow would be emitted to the ambient environment. Nowadays, we are paying high attention to the influence of lubricating liquid and cooling liquid on the health of operators during minimal quantity lubricant machining, e.g., the operators may suffer from various respiratory system diseases including occupational asthma, allergic pneumonia and lung dysfunction and skin diseases such as allergy, oil acne, skin cancer and the like. Latent health hazards brought to the operators by fog drops using air as power are industrially concerned in minimal quantity lubrication. When compressed air is used as power of spraying in the minimal quantity lubrication, the sprayed fog drops are no longer constrained, the motion of the fog drops are no longer controllable, and a series of problems such as diffusion, drift and the like are produced. However, due to these problems, the minimal fog drops are diffused to the working environment, to cause great pollution to the environment and great health hazard to workers. When the fog drops are less than 4 μm, various occupational diseases are even caused. According to practical reports, even if the workers are exposed in such an environment for a short time, the lung function may also be destroyed. Thus, the National Institute for Occupational Safety and Health in the United States suggests that the exposure limit concentration of mineral oil fog drops is 0.5 mg/m3. To ensure the health of the workers, the minimal liquid drops in the minimal quantity lubrication process must be controlled, to reduce the diffusion quantity. However, in view of the existing retrieved documents, researches on such aspect have not been reported, so researches on the above problems are extremely urgent. Based on the current situation, controllable distribution of the minimal fog drops in the minimal quantity lubrication process is explored.